U.S. Pat. No. 3,949,229 entitled, X-ray Scanning Method and Apparatus, issued Apr. 6, 1976 to the present applicant, discloses a scanning X-ray system for producing high quality radiographic images, instantaneously if desired, with substantially less radiation dosage of a subject than is required by older radiographic techniques which use X-ray film or florescent screens.
The scanning X-ray system of U.S. Pat. No. 3,949,229 includes an X-ray source generating a moving X-ray origin point which is swept along successive spaced apart scan lines of a raster pattern area. A radiation detector is situated at the opposite side of a subject to be examined. Output signals from the detector modulate the electron beam intensity within a cathode ray display tube such as an oscilloscope, a television receiver or the like. The beam sweep raster pattern of the display tube is synchronized with that of the X-ray source to produce an instantaneous visible radiographic image of internal regions of the subject. The output signals of the detector together with the sweep frequency signals from the X-ray source may also be stored on magnetic tape or the like for later reproduction of the image.
A scanning X-ray system of the particular kind disclosed in prior U.S. Pat. No. 3,949,229 is capable of producing an image without using a collimator or X-ray focusing device between the X-ray source and the detector but as a practical matter usage of a collimator is desirable under many circumstances. The collimator is typically a body of X-ray absorbent material which is situated between the X-ray source and the subject and which has rows of small radiation transmissive passages which are directed towards the detector.
The collimator reduces radiation dosage of the subject by suppressing X rays which are not directed toward the small detector and which therefore could not contribute useful information to the image. The collimator also enhances image clarity by reducing secondary X-ray production at random origin points within the subject.
The scanning X-ray system of the above identified U.S. patent was designed primarily for medical and dental examinations although it is also useful for other purposes such as in the quality checking of metallurgical castings or other manufactured parts. In some of these usages, and very notably in connection with dental examinations, positioning of the scanning X-ray apparatus in preparation for an examination of a subject may be time consuming and may require complicated and taxing operations.
To select and define the region of the subject which is to appear in the image, a radiation detector must be carefully positioned and then fixedly supported at one side of the region which is to be examined and the collimator must be positioned and then supported at the other side in an orientation at which the collimator passages are directed towards the detector.
The particular form of scanning X-ray system described in prior U.S. Pat. No. 3,949,229 uses one or more detectors which are very small in relation to the X-ray origin point raster area at the X-ray source. This requires use of a focusing collimator in which the radiation transmissive passages are convergent towards a distant focal point which may be the location of the detector. Consequently, the detector and collimator must not only be precisely positioned relative to the subject but also with respect to each other. As the passages of the collimator are convergent, there is a specific alignment and a particular spacing or narrow range of spacings which must be established between the detector and the collimator in order that X rays which are transmitted through the different portions of the collimator will all be intercepted by the small detector.
Some other forms of scanning X-ray system, such as those disclosed in prior U.S. Pat. No. 2,730,566 issued Jan. 10, 1956 to J. B. Bartow, et al and entitled, Method and Apparatus for X-ray Fluoroscopy, employ a bulky detector at least as broad as the X-ray raster pattern area of the X-ray source. Consequently, such systems may use a non-focusing collimator in which the radiation transmissive passages are parallel rather than being convergent. Because of the absence of a finite focal point, the particular matter of spacing of the detector from the X-ray source may not be so critical in such systems but the other positioning and orientation problems discussed above, in arranging the detector and collimator to image a selected region, can still be encountered.
Difficulties in positioning and then supporting the detector and collimator in a selected relationship to the subject and also in a selected relationship to each other tend to be particularly pronounced in connection with dental X-ray examinations since the detector together with means for transmitting the X-ray count signals from the detector must often be situated inside the mouth of the dental patient.
In the scanning X-ray systems as disclosed in the above identified prior U.S. patents, the collimators are usually secured to the face of the X-ray source itself. Positioning of the collimator for image selection therefore requires careful maneuvering of the relatively bulky and heavy X-ray source itself. The detector is movable independently of the source and is supported by essentially independent means. Consequently, the supports and positioning means do not inherently establish the detector and collimator positions, alignments and spacings necessary to image a selected region of the subject. These must be arrived at by trial maneuverings of both the detector and the heavy collimator-source assembly relative to the subject and relative to each other.
The complications of positioning and supporting the apparatus in preparation for a radiographic examination are greatly alleviated by a source, collimator and detector construction disclosed in applicant's copending U.S. application Ser. No. 803,077 filed June 3, 1977 and entitled, Scanning Radiographic Apparatus and Method. In that construction, both the collimator and the detector are attached to the face of the X-ray source itself forming a unitized assembly in which the necessary alignments and spacings of the collimator relative to the detector are inherently fixed. More specifically, the detector is situated in a removable rigid probe which extends forwardly from the face of the source to maintain the detector at the point at which it intercepts the X rays which are transmitted through the passages of the collimator. Thus, in setting up for an examination, the dentist, dental technician or other operator need not be concerned about positioning or orientation of the detector relative to the source and collimator but instead simply maneuvers all three components as a unit relative to the subject to select the region of the subject which is to appear in the image.
Further simplification of the process of setting up for an X-ray examination would be highly desirable. Precise maneuvering and positioning of the unitized X-ray source, collimator and detector probe described above can be somewhat taxing under some circumstances, primarily because of the inclusion of the heavy and bulky X-ray source in the unit. In the case of dental examinations where the protruding detector probe extends into the mouth of the patient, inprecise or undesirably abrupt movements of the unit can cause patient discomfort or other undesirable effects. Also, the presence of the bulky X-ray source in front of the patient's face during the image selection process restricts visibility of the patient's dentition. Somewhat similar problems may be encountered in usage of such apparatus for certain nondental applications. Where the probe must be maneuvered into a constricted passage within a metallurgical casting, for example, inadvertent abrupt movements of the heavy unitized apparatus can result in damage or breakage of the detector probe.
Setting up of a scanning X-ray system of this general kind for dental examinations and for certain other radiographic operations as well would be facilitated by reducing the bulk and weight of the apparatus which the operator must maneuver, position and then fixedly support in order to select and fix the region of the subject to be imaged.